As new generations of wireless communication devices become smaller and packed with more multi-band functions, designing antenna systems for such devices becomes more challenging. In particular, a communication device with an air interface tends to be affected by use conditions such as the presence of a human hand, a head, a metal object and other interference-causing objects placed in the vicinity of an antenna, resulting in impedance mismatch at the antenna terminal. Designing internal antennas for devices that have partial or complete metallized back covers, such as a metal back cover on a cell phone or tablet adds an additional parameter that needs to be optimized if good antenna performance is to be maintained. Accordingly, novel antenna design techniques are needed to provide efficient antenna performance for internal antennas when integrated into communication devices that have metallized housings or covers. Ideally, these novel techniques need to have little or no impact on the aesthetics of the industrial design.
The term “NFC” refers to near field communication that achieves communication by electromagnetic induction using a frequency in the 13.56 MHz band. This low frequency required the use of large coil acting as antenna radiator. In typical devices, such as mobile devices or laptop, these antenna radiators are provided with a magnetic sheet that improves the communication efficiency in the 13.56 MHz band, and are mounted in the back cover of the device.
Such solution works well for devices using a non-conductive material for the back cover, such as plastic. However for devices using metalized enclosure or back cover, these solutions are inefficient as most of the magnetic field created by the radiator is concealed within the metallic enclosure.
Some solutions to the problem have been proposed, using different type of slot or opening in the cover to allow the magnetic field to leak out by these apertures. These solutions all add important constrains regarding the device's aesthetic.
Besides the points mentioned above, in a device such as a mobile phone, mounting the NFC antenna in the back cover requires the user to change his hand grip on the device as the back cover of the mobile phone is usually facing the palm of the hand when the user is browsing, typing or using an application. So if an application needs to use the NFC interface, the user has to modify his hand grip on the mobile phone in order to position the back of the mobile phone toward the NFC tag or reader that the application wants to communicate with.
Therefore, solutions to the problems mentioned above are needed.